Packet-oriented features like High-Speed Downlink Packet Access (HSDPA) and Enhanced Uplink (E-DCH) in Universal Mobile Telecommunication Network Systems (UMTS) with radio access networks applying code-division multiple access schemes will promote the subscribers, desire for continuous connectivity, which implies that users stay connected over a long time period, however, with only occasional active periods of data transmission, and avoiding frequent connection terminations and re-establishments with the inherent overhead and delays. This is the perceived mode that a subscriber is used to in fixed broadband networks (like, e.g., DSL) and a precondition to attract users from such fixed broadband networks.
In order to support a high number of HSDPA-users in the code limited downlink, a fractional downlink physical channel (F-DPCH) has been introduced Release 6 of the specifications for UMTS issued by the 3rd Generation Partnership Project (3GPP). On the other hand, for the uplink, it has been observed that the limiting factor for supporting a similarly high number of E-DCH users is the noise rise. If it can be assumed that many users during at least certain time periods are not transmitting any user data (e.g. when reading during a web browsing session or in between packets for periodic packet transmissions such as VoIP), the corresponding overhead in the noise rise caused by maintained control channels will significantly limit the number of users that can be efficiently supported.
As a complete release of dedicated channels during periods of traffic inactivity would cause considerable delays for re-establishing data transmission and a corresponding bad user perception, the impact of control channels on uplink noise rise is to be reduced while maintaining the connections and allowing a much faster reactivation for temporarily inactive users. This is considered to contribute to a significant increase of the number of packet data users (i.e. HS-DSCH/E-DCH users without UL DPDCH) in the UMTS FDD system that can stay in the CELL_DCH state over a long time period without degrading cell throughput and that can restart transmission after a period of inactivity with a much shorter delay (<50 ms) than would be necessary for re-establishment of a new connection.
In the uplink direction, several channels from each user equipment will be transmitted with the introduction of the enhanced uplink as illustrated in FIG. 1. The DPCCH carries pilot symbols and parts of the outband control signaling. Remaining outband control signaling for the enhanced uplink is carried on the E-DPCCH, while the E-DPDCH carries the data transmitted using the enhanced uplink features. The HS-DPCCH carries positive and negative acknowledgements (ACK/NAK) related to the HSDPA downlink transmissions and Channel Quality Indicators (CQI) to inform the radio base station, e.g. the NodeB, about the downlink channel conditions experienced by a particular user equipment.
Similarly to the uplink in earlier releases of the WCDMA standard, the enhanced uplink uses inner and outer loop power control (OLPC). The power control mechanism ensures that a user equipment does not transmit with higher power than required for successful delivery of the transmitted data (possibly using multiple transmission attempts). This ensures stable system operation and efficient radio resource utilization. Further, uplink DPCCH gating described in 3GPP TR 25.903, “Continuous Connectivity for Packet Data Users”, is considered to be an enhancement of E-DCH and HSDPA and a further means to reduce the uplink noise rise while serving greater numbers of users. The basic principle with UL DPCCH gating is that the user equipment automatically stops the continuous DPCCH transmission if there is neither E-DCH nor HS-DPCCH transmission and applies a known DPCCH activity (DPCCH on/off) pattern. When an E-DCH or HS-DPCCH transmission takes place also the DPCCH is transmitted regardless of the activity pattern. Examples for DPCCH gating patterns are shown in FIGS. 3a and 3b, considering TTIs of 2 ms and 10 ms. FIGS. 3a and 3b illustrate two examples of gated DPCCH transmissions assuming 2 ms subframes and HARQ-process numbers as illustrated in 31. The example in FIG. 3 assumes a gated transmission with 3 slots on and 45 off while FIG. 3b assumes a gated transmission with 3 slots on but 27 slots off. An E-DCH VoIP activity example is shown in 32, DPCCH transmission during voice inactivity in 33 and DPCCH transmission during voice activity in 34 whereby subframes with transmission are illustrated by a marking whereas subframes without transmission are not marked.